In the past, to form a cast or molded article with internal threads, the article would be cast with a hole which was then tapped using a tool to cut the internal threads in the hole. Accordingly, this process required two steps, which meant more time and labor to produce an article with internal threads.
This led to the development of numerous die casting machines for casting an article with an internally screw-threaded bore in a single step. There are, however, several disadvantages to many of these die casting machines employed by the prior art. For example, many of the drive mechanisms merely rotated the core pin so that the newly formed threads would drive the core pin out of the mold. Accordingly, this type of an arrangement places great stress on the newly formed threads, and thus may cause the threads to be damaged while withdrawing the core pin. Moreover, many of the drive mechanisms of the prior art are quite complex, using hydraulic pistons, many gears and other parts.
Examples of these prior art devices are disclosed in U.S. Pat. Nos. 2,579,952 to Morin; 3,905,416 to Hammer; 4,079,475 to Thompson; 4,240,498 to Frenette; 4,280,549 to Gibbs; 4,554,962 to Wright; and 4,633,932 to Ferguson. A further example is disclosed in Canadian patent No. 983,666.
In view of the above, it is apparent that there exists a need for a way to remove the core pin without damaging the newly formed internal threads. Accordingly, this invention addresses this need in the art, along with other needs which will become apparent to those skilled in the art once given this disclosure.